The present invention concerns a local mobile access network.
Local mobile access networks are already known, reference is made for example to the patent document FR-A-2 714 559 which describes such a network consisting of a double terminal on which radio terminals are interconnected, for example, by the use of concentration nodes, to which other mobile stations can be connected.
In time, communications between mobile units or between a mobile unit and another source will not only be phonic but will require transport of representative data, e.g. still or animated images which justify the use of multi-output or even wideband networks. By nature, the ATM (Asynchronous Transfer Mode) technology ensures the transport of all kinds of information to various outputs.
A first object of the invention is to propose a local mobile access network which supports this ATM technology.
The growing demand for communication services between mobile units increases the traffic density that must be able to serve each radio terminal of the local access network. In order to ensure a better radio coverage in urban areas while taking the necessarily limited performances of said radio terminals into account, the coverage of each radio terminal must be reduced and microcellular networks proposed. Nevertheless, this poses the problem of a very significant multiplication of signalling procedures, notably when mobile units transfer from the radio coverage of one terminal to that of another terminal. This multiplication is also brought about by known phenomena, such as xe2x80x9cfrom the street cornerxe2x80x9d or of xe2x80x9cthe passing truckxe2x80x9d. The Intercellular Automatic Transfers (TAI), still called xe2x80x9chand-over phasexe2x80x9d in the technical field, generate processing procedures that may rapidly saturate the control devices of the terrestrial network.
The object of the invention is therefore to propose an access network based on the ATM technology that would enable one to solve this particular problem due to the capability of these networks to very flexibly and extremely quickly manage the support links identified by virtual connections.
A local mobile access network according to the invention is of the kind that comprises a distribution network made up of a plurality of nodes, each node being connected to a concentrator which is connected to at least one radio terminal designed to communicate with mobile units connected to said terminals, at least one of said nodes of said distribution network being connected, via routing equipment, to a virtual channel switch.
In order to attain the aforementioned objects, it is characterized therein that each virtual connection established between a mobile unit and said switch is identified for the entire duration of the communication, no matter which radio terminal is connected to said mobile unit, by a unique virtual channel identifier for the user cells and a unique virtual channel identifier for the signalling cells and therein that, during the hand-over phases, when a mobile unit is connected to two radio terminals, said two terminals can exchange information, which is then transmitted by cells carrying the signalling channel identifier allocated to said mobile unit.
According to another characteristic of the invention, said information which is transmitted between said two terminals during said hand-over phases is transmitted by cells carrying the signalling channel identifier allocated to said mobile unit and a virtual channel identifier corresponding to a common virtual channel defined in the distribution network according to point-to-point-with-fusion type of topology in the ascending direction and point-to-multipoint-with-diffusion in the descending direction.
According to another characteristic of the invention, the information that is transmitted between the said two terminals during the said hand-over phases is transmitted by cells carrying the signalling channel identifier allocated to said mobile unit and a virtual channel identifier corresponding to a common virtual channel defined in the distribution network according to virtual ring topology.
Thus, unlike the known mobile access networks, the processing procedures of the hand-over phases is distributed in the network.
According to another characteristic of the invention, each concentrator reaches the said virtual ring without passband reservation or, on the contrary, with passband reservation. In the latter case, said network is equipped with a control element for the passband designed to emit reservation cells corresponding to the output of the band to be reserved, a concentrator to emit a message capturing at least one of said cells and replacing it or them by one or several cells containing said message, a concentrator designed to receive a message replacing the cell or cells containing said message by one or several reservation cells.
According to another characteristic of the invention, each virtual connection established for a communication is, moreover, identified by a first virtual channel identifier when said communication is local and thus concerns two mobile units linked to one or more terminals of said network and by a second virtual channel identifier when said communication is incoming or outgoing and thus involves two speakers, of which only one is a mobile unit linked to one or more terminals of said network.
According to another characteristic of the invention, during hand-over phases, the two terminals linked to the mobile unit can make identification marks and erase said marks in the concentrators to which they are respectively connected.
According to another characteristic of the invention, servers that are accessible by permanent connections of the virtual channel type are interconnected to the routing equipment. Among said servers, one is a macrodiversity server active on each ascending virtual connection. Also included among said servers is a transcoder which carries out format transcoding of the cells having a virtual channel identifier identifying an incoming or outgoing communication.
The invention also concerns the architecture of said local access network. For example, said nodes of said distribution network are linked two by two in such a way so as to form a simple or double contrarotating ring. Said nodes of said distribution network are arranged in contraparallel double segments, one end of which is connected to the virtual channel switch. At least one of said segments may include sub-segments, one of the ends of which is connected to said segment via a repeater.
According to an advantageous characteristic, a local mobile access network according to the invention consists of a plurality of concentration nodes and of a switching and control centre, each concentration node consisting of a concentrator to which a plurality of radio terminals can be linked and a node connected to said concentrator, said node being a node of the distribution network, the said switching and control centre comprising the said routing equipment, said switch and at least one of the nodes of the distribution network. Said switching and control centre may, moreover, comprise at least one server.